Modbus exception code


Thread Starter

Prasanth M V

Hi Friends,

From the Protocol Specification i understood that, ACKNOWLEDGE(0x05) is sent by the Slave device to Master, when it takes more time to perform the requested operation.

In response, to that Master can next issue a Poll Program Complete message to determine if processing is completed.

What is mean by "Poll Program Complete message" as described in Modbus_Application_Protocol_V1_1b.pdf, Page No: 49.

Prasanth M V
Software Engineer,
Ushus Technologies
311, Nila,Technopark, Trivandrum - 695581, Kerala, India
That message is part of the Schneider PLC programming command set. Programming commands are not defined in the Modbus specification.

Lynn August Linse

More importantly, I can promise that no SCADA or OPC tool will be happy to see such a response. They will just detect "the unknown exception" and put the unit off-line.

Now if you are doing 'programming' of your own product via Modbus, then you are free to make your HOST and embedded system do as they please, just do not expect other third-party tools to react as expected to such vendor-specific exception codes (despite them being in "the standard").